Genetics is the study of how traits are inherited in offspring.

Gene: Segment of chromosome (DNA) that codes for a trait

Allele: Different form of the same gene.

Example: Skin Color (Color, Albino)

Humans normally have two alleles for each gene.

Dominant: Trait that gets expressed from dominant allele.

Phenotype: Observable physical or behavioral trait

Genotype: Genes (Alleles) that code for a trait

Homozygous: having the same forms (alleles) for a gene on both chromosomes.

Also said to be purebred.

Homozygous Dominant = AAHomozygous Recessive = aa

Heterozygous: having different forms (alleles) for a gene on both chromosomes.

Also said to be hybrid.

Monohybrid CrossesGene: Albinism

Dominant Allele: A = normal skin color

Recessive Allele: a = albino

Heterozygous = Aa, or aA

Cross a heterozygous individual with a heterozygous individual: Aa X Aa

Heterozygous = Aa, or aA

A aA AA Aaa Aa aa

Cross a homozygous dominant individual with a homozygous recessive individual: AA X aa

Heterozygous = Aa, or aA

A Aa Aa Aaa Aa Aa

Test Cross: Cross a homozygous recessive individual with an unknown (homozygous dominant or heterozygous): aa X A?

Heterozygous = Aa, or aA

A ?a Aa A?a Aa A?

The outcome determines the offspring. If half of the offspring are albino, then the unknown is heterozygous (Aa).

Heterozygous = Aa, or aA

A aa Aa aaa Aa aa

If all of the offspring have normal skin color, then the unknown is homozygous dominant.

Heterozygous = Aa, or aA

A Aa Aa Aaa Aa Aa